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<head>
  <meta charset="UTF-8">
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  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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  </style>
</head>

<body>
  <a href="">你好</a>
  <script>
    const a = document.querySelector('a')
    a.style.fontSize = '30px'
    a.className = 'hello'
  </script>
</body>

</html>